Uncertainty estimation to evaluate mass balances on a combustion system |
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Authors: | Paula Teixeira Helena Lopes Ibrahim Gulyurtlu Nuno Lapa |
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Institution: | (1) LNEG, Estrada do Pa?o do Lumiar, 22, Ed. J, 1649-038 Lisbon, Portugal;(2) UNL-FCT-DCTB-UBiA, Quinta da Torre, 2829-516 Caparica, Portugal |
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Abstract: | Mass balances of ash and potassium for a fluidized bed combustor were performed incorporating measurement uncertainties. The
total output mass of ash or a chemical element should be equal to the mass in the input fuel; however, this is not often achieved.
A realistic estimation of recovery uncertainty can support the reliability of a mass balance. Estimation of uncertainty helps
to establish a reliable evaluation of the recovery ratio of ash mass and elemental mass. This may clarify whether any apparent
lack in closing the mass balance can be attributed to uncertainties. The evaluation of measurement uncertainty for different
matrices, namely coal, biomass, sand and ashes from different streams was based on internal quality control data and external
quality control data, namely analysis of samples from proficiency tests or use of a certified reference material. The evaluation
of intermediate precision and trueness allowed the estimation of measurement uncertainty. Due to the different physic and
chemical characteristics of the studied matrices, the uncertainty of precision was evaluated using R-charts of data obtained
from the analysis of duplicates for the majority of samples. This allowed evaluating sample heterogeneity effects. The instrumental
acceptance criterion was also considered and included in the combined uncertainty. The trueness was evaluated using data from
several proficiency tests and from analysis of a certified reference material or sample spiking. Statistically significant
bias was included. |
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